It is often desirable to use personal listening devices when listening to music and other audio material, in order to not disturb others that are nearby. For example, users often use headphones, such as a wired headset or a wireless headset, when listening to music that is being played back from a portable music player, or when conducting a conversation with another user during a voice or video telephony call. Some times, over the ear earphones are used, particularly in environments in which size or bulk is not a major concern. When a more compact profile is desired, users often elect to use in-ear headphones, some times referred to as earbuds.
In order to provide a form of passive barrier against ambient noise, headphones are often designed to form some level of acoustic seal with the ear of the wearer. With loose fitting earbuds, however, the audio frequency response and the overall quality of the desired user audio content that is heard varies substantially from user-to-user. This is due to different degrees of acoustic seal that is achieved around an earpiece speaker against the ear. This may be due to several reasons, including geometrical variations of the ear shapes, and placement variation due to physical activities while using the earpiece, for example, shifting of loose fitting earbuds during walking or running or simply during certain positions of use such as while lying down.
A certain amount of acoustic leakage, that is leakage of the ambient noise into the ear canal, may be built into the earphone by design, to avoid the feeling of acoustic occlusion and also for improving comfort (relative to a tightly or completely sealed earphone design). However, a leaky acoustic design often results in the undesirable effect of inconsistent low frequency or bass response, between different users and in different wearing positions. In addition, the leaky acoustic design also has poor passive acoustic attenuation which leads to generally lower quality user experience of the desired user audio content, due to low signal-to-noise ratio or low speech intelligibility in environments with high ambient or background noise levels.